POOLE, ENGLAND—Science Magazine reports that human and giant ground sloth footprints estimated to be between 10,000 and 15,000 years old have been found in New Mexico’s White Sands National Monument. Sedimentologist Matthew Bennett of Bournemouth University said sloth trackways are usually straight or slightly curved, but when human prints are also found nearby, a sloth’s path sometimes turns sharply or indicates the animal reared up on its hind legs in order to use its front limbs and sharp claws for defense. Bennett and his colleagues suggest this trackway records a human pursuit of a sloth that weighed up to 2,000 pounds. In this scenario, the hunters extended their strides in order to step into the sloth’s footprints, until it reared up on its hind legs. This trackway also has “flailing circles,” which are left behind when an animal swivels around while attempting to protect itself from something in the environment. But critics question whether the humans who left these prints were actually hunting the sloth, suggesting that they may have instead found the fresh prints and decided to walk in them after the sloth had moved on. For more on Bennett's study of ancient footprints, go to “Proof in the Prints.”